Polyimide balloon catheter and method of making same

ABSTRACT

A thin wall balloon for a balloon catheter is formed by depositing a film (such as polyimide) over a substrate which has an exterior surface configuration corresponding to a desired shape of the balloon in an inflated (or deflated) condition. After the polyimide film is cured, the substrate is removed from within the polyimide film by chemically dissolving the substrate.

This is a continuation of application Ser. No. 08/101,349, filed Aug. 2,1993, (now abandoned), which is a continuation of application Ser. No.07/847,799, filed Mar. 6, 1992 (now abandoned), which is a division ofapplication Ser. No. 07/798,851, filed Nov. 18, 1991, now issued as U.S.Pat. No. 5,207,700, which is a continuation of application Ser. No.07/617,430, filed Nov. 26, 1990 (now abandoned), which is a continuationof application Ser. No. 07/364,116, filed Jun. 12, 1989 (now abandoned),which is a division of application Ser. No. 07/229,313, filed Aug. 8,1988, now issued as U.S. Pat. No. 4,952,357.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to balloon catheters useful in medicaldilatation procedures.

2. Description of the Prior Art

Angioplasty has gained wide acceptance in recent years as a efficientand effective method for treating types of vascular diseases. Inparticular, angioplasty is widely used for opening stenoses in thecoronary arteries, and is also used for treatment of stenoses in otherparts of the vascular system.

The most widely used form of angioplasty makes use of a dilatationcatheter which has an inflatable balloon at its distal end. Usingfluoroscopy, the physician guides the catheter through the vascularsystem until the balloon is positioned across the stenosis. The balloonis then inflated by supplying fluid under pressure through an inflationlumen to the balloon. The inflation of the balloon causes stretching ofthe artery and pressing of the lesion into the artery wall toreestablish acceptable blood flow through the artery.

In order to treat very tight stenosis with small openings, there hasbeen a continuing effort to reduce the profile of the catheter so thatthe catheter not only can reach but also can cross such a very tightstenosis. An important factor in the profile of the dilatation catheteris the wall thickness of the balloon material.

Balloons for dilatation balloon catheters have been made from a widevariety of polymeric materials. Typically the balloon wall thicknesseshave been on the order of 0.002 to 0.003 inches with most materials.There have been continuing efforts, however, to develop thin wallballoon materials which have much thinner walls than the standard wallthicknesses (and thus are capable of lower profile) while still havingthe necessary distensibility and burst pressure rating. One example of athin wall balloon is described in the Levy U.S. Pat. No. 4,490,421. Inthe Levy patent, molded balloons made of a polyethylene terephthalate(PET) homopolyester are described. PET-balloons having wall thicknesseson the order of 0.0002 inches have been developed.

Despite the advantage of very thin walls, PET balloons have been foundto have a number of significant disadvantages. First, PET balloonsformed by blow molding can exhibit pinholes which can emit a highvelocity jet of inflation fluid during inflation. This jet can causeartery dissection. Second, PET exhibits low tear resistance. Third, PETballoons will not distend more than about 5%, so that higher inflationpressures will not allow the physician to fully open a stenosis if theballoon proves to be slightly smaller than what is needed. Fourth, PETballoons are very susceptible to damage, and can not be touched. Fifth,PET will not take a crease ( which is advantageous for folding theballoon).

There is a continuing need for improved balloon catheters and, inparticular, for alternative thin wall balloon materials and fabricationmethods.

SUMMARY OF THE INVENTION

A thin wall balloon for use in a balloon catheter is formed bydepositing a film (preferably a polymer film such as polyimide) over theexterior surface of a substrate which has an exterior surfaceconfiguration corresponding to the desired shape of the balloon in apredetermined condition. The film is then cured, and the substrate isremoved from within the film, leaving the finished balloon.

In one preferred embodiment of the present invention, the substrate isremoved by chemically dissolving the substrate. The substrate ispreferably a glass material, and an acid (such as HF) is used to attackand dissolve the glass material without affecting the film.

The balloon of the present invention features a very thin wall, withvery close control over the inside diameter of the balloon and with wallthicknesses which are uniform throughout the balloon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a balloon catheter using the balloon ofthe present invention.

FIGS. 2A-2C illustrate a preferred method of forming the dilatationballoon of the present invention.

FIGS. 3A and 3B illustrate a balloon formed in a normal deflated stateand inflated in a pressurized state.

FIG. 4A is an enlarged cross-sectional view of a portion of the wall ofa balloon of the present invention, having an outer layer ofantifriction material thereon.

FIG. 4B is an enlarged cross-sectional view of a portion of the wall ofa balloon of the present invention, having a plurality of layers ofmaterial defining that wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows dilatation balloon catheter 10, which has an elongatedflexible shaft 12 with inflatable thin wall balloon 14 mounted at itsdistal end. In FIG. 1, balloon 14 is shown in its fully inflatedcondition. Extending out the distal end of balloon 14 is flexible distaltip 16. Depending upon the particular construction of catheter 10, tip16 may be the distal end of a movable guidewire which extends throughshaft 12 and balloon 14, or may be the distal end of a fixed wire orcore which is bonded to balloon 14.

Shaft 12, which is preferably a metal or polymeric tube, has at leastone lumen extending from its proximal to its distal end. Depending uponthe particular construction of catheter 10, multiple lumens may beprovided in shaft 12. In any case, at least an inflation lumen extendsthrough shaft 12 for selective inflation and deflation of balloon 14.

Balloon 14 is a thin wall balloon (preferably of a polymer material suchas polyimide) which has a proximal waist portion 18 bonded to the distalend of shaft 12, an intermediate inflatable balloon section 20 of alarger diameter than waist section 18, and a smaller distal end section22. The wall thickness of balloon 14 is less than about 0.001 inches,and is preferably on the order of about 0.0003 inches. This extremelythin wall characteristic provides a very low profile for ballooncatheter 10.

Polyimide is a heterochain polymer made of two base monomers, a diamineand dianhydride (e.g. para-aminoanaline and pyromellitic dianhydride).Polyimide is typically formed by two step reaction like the followingexample. First, a polyamine is formed from the monomers. The reactionproceeds at about 25° C. and the product is soluble and stable in verypolar solvents. Second, the polyamine is condensed to polyimide at about120° C. to crosslink chain, drive off water and the remaining solvent.Further description of polyimides and their preparation can be found inAndrova et al, Polyimide, A New Class of Heat-Resistant Polymers, pp4-13, (1969), which is hereby incorporated by reference.

FIGS. 2A-2C illustrate the method of the present invention for formingpolyimide balloon 14. As shown in FIG. 2A, substrate 30 is provided withan exterior surface of configuration which will determine the innersurface of balloon 14. This surface configuration corresponds to thedesired interior surface configuration of balloon 14 when balloon 14 isfully inflated. In preferred embodiments of the present invention,substrate 30 is a material formed of a glass resin. As shown in FIG. 2A,substrate 30 has a central passage 32 extending axially through it, andhas a proximal waist section 34, a balloon section 36 of greater outsidediameter, and a distal tip section 38 of reduced outside diameter.

As shown in FIG. 2B, polyimide film 40 is deposited on the exteriorsurface of substrate 30. This step can be performed, for example, bydipping substrate 30 into thin polyamine solution and then heatingsubstrate 30 and the deposited solution to form polyimide film 40. Eachdeposition formed with this technique is about 0.0001 inches thick. Inpreferred embodiments of the present invention, repeated dip coatingsand heat curing is performed until the desired thickness of film 40 hasbeen formed. In preferred embodiments, this thickness is on the order ofabout 0.0003 inches.

The next step in the process is the removal of substrate 30 from withinthe deposited polyimide film 40. Removal is preferably achieved byplacing substrate 30 and film 40 into an HF acid bath to etch away glasssubstrate 30. Polyimide film 40 is not affected by the HF acid. FIG. 2Cshows balloon 14 after substrate 30 has been completely removed.

The present invention has several important advantages. First, it offersextremely thin walls, and therefore is extremely well suited for lowprofile catheters. Second, the process of the present invention, asillustrated in FIGS. 2A-2C, offers close control over the insidediameter tolerances of balloon 14. Third, the method of the presentinvention, unlike other balloon fabrication techniques, yields a balloonhaving walls of uniform wall thickness throughout the entire balloon(i.e. waist 18, balloon 20 and distal section 22). Fourth, whenpolyimide is the polymer material deposited, the resulting balloon hasthe benefit of superior material properties compared to PET, such ashigher tear resistance, greater strength and toughness, lesssusceptibility to damage, and the ability to take a crease (so that theballoon can be preformed to fold down when deflated).

Other advantageous features can be obtained using other embodiments ofthe present invention. For example, as illustrated in FIG. 4A, layers ofdifferent materials can be deposited to form the balloon 14. In oneembodiment, an antifriction coating is deposited as a final outer layerof the balloon. A suitable coating material (which provides antifrictioncharacteristics without significantly increasing wall thickness) isParalene C, with a thickness of about 1500A or less.

In another embodiment, a thin metal layer (e.g. layer 45 in FIG. 4B) isdeposited between polymer layers (e.g. layers 45 and 47 in FIG. 4B) oras an inner layer or outer layer (layer 47) . This offers a capabilityof applying localized heat at the stenosis during inflation by directingRF energy (or another form of electrical or electromagnetic energy) tothe metal layer.

In still another embodiment, a colorant is added to one or more layersdeposited to form the balloon. The colorant is capable of absorbingenergy (e.g. radiation from a laser beam directed through the catheterto the balloon) for applying localized heat.

In the preferred embodiment of the method of the present inventiondescribed in FIGS. 2A-2C, substrate 30 has a surface configuration whichcorresponds to the desired shape of the balloon in a fully inflatedcondition. Conversely, the surface configuration of substrate 30 cancorrespond to the desired shaped of the balloon in a deflated condition(or in a partially inflated condition). This latter embodiment isparticularly advantageous for ensuring that the balloon has a minimumprofile when deflated by making the shape of the deflated balloonpredictable. By using this embodiment, creasing and heat settingcharacteristics may not be required. FIGS. 3A and 3B illustrate anexample of this embodiment. FIG. 3A is a cross section of balloon 50 ina deflated condition, which has been defined by substrate 52 havingthree lobes 54A-54C. As a result, ,balloon 50 has three correspondinglobes 56A-56C when deflated. FIG. 3B shows the fully inflated state ofballoon 50.

Other and alternative steps can be used with the present invention. Forexample, depending upon the particular material being deposited, avariety of different deposition techniques can be employed, includingdip coating, vapor deposition, electroplating, and sputtering.

Similarly, although chemical removal of the substrate is preferred,other techniques are also possible. For example, when the substrate hasa melting temperature which is lower than that of the deposited layer(or layers), the substrate can be removed by heating the substrate toits melting temperature.

Finally, when polyimide is used as the polymer material, the two stageprocess used to form the polyimide offers an opportunity to performintermediate processing. When the layer is in the polyaminoacid state(i.e. prior to final cure), it is more amenable to mechanical formingsuch as stretching, necking and drawing/orientation steps. These stepsare preferably performed prior to the final cure.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A dilatation balloon catheter for applyingpressure and heat to a stenosis within a patient's artery comprising:ashaft having an inflation lumen extending therethrough from a proximalend to a distal end; and a thin-walled inflatable balloon at the distalend of the shaft, the balloon being in fluid communication with theinflation lumen and being defined by a wall having a wall thickness ofless than about 0.001 inches, a substantial portion of which is formedof polyimide polymer material, including an innermost polyimide layerdefining an inner surface of the balloon, and an outer layer of ananti-friction material having a thickness of no greater than about 1,500Angstroms, an intermediate metal film layer formed by deposition whichheats in response to an application of electromagnetic energy thereto toapply heat radially outward to the stenosis while the balloon isinflated; wherein the balloon has a proximal section connected to thedistal end of the shaft, an intermediate inflatable section, and adistal section.
 2. The dilatation balloon catheter of claim 1 whereinthe balloon has a wall thickness of about 0.0003 inches.
 3. Thedilatation balloon catheter of claim 1 wherein the balloon has strengthand tear resistance properties which are determined by the layers ofpolyimide polymer material.
 4. A dilatation balloon catheter forangioplasty, the catheter comprising:an elongated flexible shaft havingan inflation lumen extending from a proximal end to a distal end; and aninflatable balloon, a substantial portion of which is formed ofpolyimide, the balloon having a proximal section connected to the distalend of the shaft, an intermediate balloon section, and a distal section,the intermediate section having an outer diameter, when inflated, whichis greater than the proximal section and the distal section, the balloonhaving a wall thickness of less than about 0.001 inches and havingstrength and tear resistance properties determined by the polyimide; andthe balloon having a deposited metal film layer which heats in responseto electromagnetic energy being applied thereto to apply heat radiallyoutward to the stenosis while the balloon is inflated.
 5. The dilatationballoon catheter of claim 4 and further comprising:an outer layer of ananti-friction material over an outermost layer of polyimide.
 6. Thedilatation balloon catheter of claim 5 wherein the outer layer has athickness of no greater than about 1,500 Angstroms.
 7. The dilatationballoon catheter of claim 4 wherein the wall thickness is about 0.0003inches.
 8. A dilatation balloon catheter for applying pressure and heatto a stenosis within a patient's artery, the catheter comprising:anelongated flexible shaft having an inflation lumen extending from aproximal end to a distal end; and an inflatable balloon having a wallthickness of about 0.0003 inches, wherein a portion of the balloon isformed of a polymeric material and including a thin continuous andgapless coating defining at least one entire contour of the inflatableballoon and consisting solely of metal formed by deposition upon anouter surface of the polymeric material, wherein the coating has alength, a width and a thickness, wherein the thickness is substantiallyuniform throughout the coating, wherein the length is larger than thewidth, and wherein the width is at least twice as large as thethickness, wherein the coating heats in response to electromagneticenergy being applied thereto.
 9. The dilatation balloon catheter ofclaim 8 and further comprising:a layer of an anti-friction material overthe portion formed of a polymeric material.
 10. The dilatation ballooncatheter of claim 9 wherein the layer of anti-friction material has athickness of no greater than about 1,500 Angstroms.
 11. The dilatationballoon catheter of claim 8 wherein the balloon has a wall thickness ofabout 0.0003 inches.
 12. The balloon dilatation catheter of claim 8wherein the deposited thin coating has a uniform thickness throughoutthe contour of the balloon.
 13. A balloon dilatation catheter forapplying heat to a stenosis within a patient's artery during dilatationof the stenosis, the balloon dilatation catheter comprising:an elongatedshaft having an inflation lumen extending between a proximal end and adistal end; and a multilayer inflatable balloon at the distal end of theshaft and having an interior in communication with the inflation lumen,the balloon including at least a portion of which comprises a polymericlayer and a deposited thin continuous and gapless coating upon an outersurface of the polymeric layer, wherein the coating defines at least oneentire contour of the inflatable balloon and consists solely of metalwhich heats in response to electromagnetic energy being applied thereto,the deposited thin coating being positioned for receiving theelectromagnetic energy and applying localized heat radially outward tothe stenosis while the balloon is inflated.
 14. The balloon dilatationcatheter of claim 13 wherein the balloon has a wall thickness of lessthan 0.001 inches.
 15. The balloon dilatation catheter of claim 13wherein the balloon includes a plurality of polymeric layers and thedeposited thin coating is located between polymeric layers.
 16. Theballoon dilatation catheter of claim 13 wherein the deposited coatinghas a uniform thickness throughout the contour of the balloon.
 17. Adilatation balloon catheter for applying pressure and heat to a stenosiswithin a patient's artery, the catheter comprising:an elongated flexibleshaft having an inflation lumen extending from a proximal end to adistal end; and an inflatable balloon, a substantial portion of which isformed by a polymeric material and including a thin continuous andgapless metal coating formed by deposition upon an outer surface of thepolymeric material, wherein the metal coating defines at least oneentire contour of the inflatable balloon and wherein the metal coatingheats in response to electromagnetic energy being applied thereto, thedeposited thin metal layer being positioned for receiving theelectromagnetic energy and applying localized heat radially outward tothe stenosis while the balloon is inflated.
 18. A method for forming athin walled inflatable balloon for use in a dilatation balloon catheter,the method comprising the steps of:providing a substrate having anexterior surface configuration which corresponds to a desired shape ofthe balloon in a predetermined condition; depositing a first liquidcoating over the entire exterior surface of the substrate, wherein thefirst liquid coating has an exterior surface corresponding to thedesired shape of the balloon; drying the first liquid coating;depositing a second liquid coating over the entire exterior surface ofthe first dried liquid coating, wherein one of the coatings is ametallic material which heats in response to an application ofelectromagnetic energy thereto; and removing the substrate within thecoatings to leave a balloon of the desired shape.
 19. The method ofclaim 18 wherein the first and second coatings are deposited by dipcoating the substrate.
 20. A dilatation balloon catheter for applyingpressure and heat to a stenosis within a patient's artery, the cathetercomprising:an elongated flexible shaft having an inflation lumenextending from a proximal end to a distal end; and an inflatable balloonhaving a wall thickness of about 0.0003 inches, wherein a portion of theballoon is formed of a polymeric material and including a thincontinuous and gapless coating consisting solely of metal formed bydeposition upon an outer surface of the polymeric material, wherein thecoating heats in response to electromagnetic energy being appliedthereto.
 21. The dilatation balloon catheter of claim 20 and furthercomprising:a layer of an anti-friction material over the portion formedof a polymeric material.
 22. The dilatation balloon catheter of claim 21wherein the layer of anti-friction material has a thickness of nogreater than about 1,500 Angstroms.